The present invention relates to a connecting rod bearing for an internal combustion engine which is configured so that a lubricant oil which is supplied to an inner circumferential surface of a main bearing supporting a crankshaft is supplied to an inner circumferential surface of a connecting rod bearing (sliding bearing) which rotatably supports a crankpin which connects a connecting rod and the crankshaft through an inner lubricant oil passage of the crankshaft, and the connecting rod bearing is constituted of a pair of semi-cylindrical bearings.
The crankshaft of an internal combustion engine is supported at a cylinder block lower portion of the internal combustion engine via a main bearing constituted of a pair of semi-cylindrical bearings in its journal part. For the main bearing, a lubricant oil which is discharged by an oil pump is fed into a lubricant oil groove which is formed along an inner peripheral surface of the main bearing through a through-port formed in a wall of the main bearing from a oil gallery formed in a cylinder block wall. Further, a first lubricant oil passage is formed to penetrate through the journal portion in a diameter direction of the journal portion, and openings at both ends of the first lubricant oil passage communicate with the lubricant oil groove. Furthermore, a second lubricant oil passage which branches from the first lubricant oil passage in the diameter direction of the journal portion and passes through a crank arm portion is formed, and the second lubricant oil passage communicates with a third lubricant oil passage which is formed to penetrate through a crankpin in a diameter direction of the crankpin. Thus, the lubricant oil which is fed into the oil groove formed in the inner circumferential surface of the main bearing through the through-port formed in the wall of the main bearing from the oil gallery in the cylinder block wall passes through the first lubricant oil passage, the second lubricant oil passage and the third lubricant oil passage to be supplied to between sliding surfaces of the crankpin and a connecting rod bearing from an outlet port at an end portion (more specifically, a lubricant oil outlet port which is present in an outer circumferential surface of the crankpin) of the third lubricant oil passage.
The lubricant oil which is fed to the connecting rod bearing portion through the journal portion of the crankshaft from the cylinder block of the internal combustion engine is likely to be accompanied by foreign matters which are present in the lubricant oil passage of each portion. It is feared that if the foreign matters accompany the lubricant oil and are fed to between the sliding surfaces of the crankpin and the connecting rod bearing, they cause damage to the sliding surface of the connecting rod bearing.
As the countermeasure against the foreign matters entering a lubricant oil, there is proposed a sliding bearing which is constituted of a pair of semi-cylindrical bearings, and adopts the configuration in which a crush relief is formed on the inner circumferential surface of the bearing adjacent to the contact portion of the semi-cylindrical bearings, a soft layer formed from a material with a low hardness such as Pb or Sn is formed on the crush relief surface, and the foreign matters included in the lubricant oil are embedded in the soft layer and caught (JP-A-2008-215563). The crush relief indicates the region with the decreased wall thickness where the bearing wall thickness of the region near the end surface in the circumferential direction of the semi-cylindrical bearing is gradually decreased toward the end surface in the circumferential direction. The position of the center of curvature of the bearing inner circumferential surface in the wall thickness decreasing region differs from the position of the center of curvature of the bearing inner circumferential surface in the other region (specified by section 3.2, DIN1497). The crush relief is formed with the intention of absorbing a positional deviation and deformation of the butt end surfaces of semi-cylindrical bearings when a pair of semi-cylindrical bearings are assembled to a connecting rod.
Thus, in the internal combustion engines of recent years, reduction in weight has been intended with the objective of enhancing fuel economy, and the connecting rods tend to be low in rigidity. Since a connecting rod reciprocally moves and elastically deforms when the internal combustion engine operates, the sliding bearing at the large end portion of the connecting rod also follows the deformation of the connecting rod, and the clearance (gap between the sliding bearing inner circumferential surface and the crankpin surface) in the horizontal direction of the sliding bearing repeats increase and decrease. In the case of the connecting rods with low rigidity in recent years, the amount of decrease of the clearance (region near the butt surfaces of a pair of semi-cylindrical bearings) in the horizontal direction of the sliding bearing is large when the reciprocal inertia force acts on the connecting rod, and the phenomenon (close-in phenomenon) has occurred, in which the bearing inner circumferential surface at the circumferential end portion of the sliding bearing and the crankpin surface are directly in contact with each other.
In the case of the sliding bearing proposed in JP-A-2008-215563, the entire surface of the crush relief is covered with the soft layer, and in its circumferential direction, the depth of it is made shallower toward both end portions. When the crankpin and the sliding bearing relatively rotate, the foreign matters in the lubricant oil, which is present between the crankpin and the sliding bearing, move in the relative rotational direction of the crankpin along the inner surface of the sliding bearing. When the foreign matters are captured in the crush relief region, the foreign matters locally gather together in the portion with a shallow depth of the crush relief, and are pushed into the soft layer by the surface of the crankpin. These foreign matters are not completely buried in the soft layer, but are in the state exposed on the surface of the soft layer.
Contact of the foreign matters exposed on the surface of the soft layer and the surface of the crankpin continuously occurs due to the close-in phenomenon at the time of operation of the internal combustion engine, and the frictional heat generation amount locally increases in the portion where the foreign matters locally gather together and are embedded. Flow and melting occur due to softening of the soft layer on the portion where foreign matters are embedded by the resultant heat generation, and when the limit of holding the foreign matters is exceeded, a number of embedded foreign matters are simultaneously fed to the inner circumferential surface of the bearing (that is, the sliding surface) of the semi-cylindrical bearing existing in the same direction as the relative rotational direction of the crankpin, and therefore, there arises the problem that seizure easily occurs.
Further, conventionally, the countermeasures can be taken, which prevents contact of the crankpin surface and the inner circumferential surface of a sliding bearing due to a close-in phenomenon by enlarging the bearing gap between the crankpin surface and the inner circumferential surface of the bearing in the region of the circumferential end portion of the bearing by forming the inner circumferential surface of the sliding bearing into an arc shape in which the inside diameter in the horizontal direction is made large with respect to the vertical direction, as disclosed in JP-10-A-325410. Thus, in the internal combustion engines of recent years, the size of the oil pump is reduced, and the lubricant oil supply amount to the inner circumferential surface of the bearing tends to be decreased. In the case of the bearing with the bearing gap being enlarged as described in JP-A-10-325410, the leakage amount of the lubricant oil from the gap increases, and insufficiency of supply of the lubricant oil to the bearing inner circumferential surface occurs. Accordingly, under present circumstances, adoption of the sliding bearing as described in JP-A-10-325410 can be said to be difficult.